1. Field of the Invention
The present invention relates to an optical pick-up device for recording or reproducing information to or from an optical disk that is provided in an optical disk device for driving optical discs (for example, CD-R/RW and DVD-R/-RW/RAM/+R/+RW) as recording media for recording a large amount of information by information processing apparatuses, such as various computer systems.
2. Description of the Related Art
An optical pick-up device in an optical disk device for driving optical disks is constructed by a combination of various components of an optical system to form a beam spot on a recording surface of an optical disk. FIG. 6 is a view schematically illustrating the general structure of a conventional optical pick-up device. In FIG. 6, reference character A denotes an actuator assembly of the optical pick-up device, reference character B denotes a semiconductor laser hologram unit for DVD, and reference character C denotes a semiconductor laser hologram unit for CD. An optical beam irradiated from the semiconductor laser hologram unit B or the semiconductor laser hologram unit C follows the light path to an object lens 102 of an actuator assembly A via optical components included in a mirror system and a lens system and then forms a beam spot on a recording surface of an optical disk.
As shown in FIGS. 7 and 8, in the actuator assembly A, one side ends of six suspension members 105 are fixed to both longitudinal end portions of a lens holder 101 for holding the object lens 102 at top, middle, and bottom positions in pairs, and the other side ends of the suspension members 105 are fixed to a supporting member 106 arranged on the rear side of a suspension holder 104 fixed to a yoke base 103. In this way, since the lens holder 101 is elastically supported by the suspension members 105 in a cantilever manner, the lens holder 101 can rock vertically and horizontally. In addition, the supporting member 106 is generally composed of a printed circuit board (PCB) having low rigidity and has a floating structure for suppressing, for example, secondary resonance generated when the lens holder is driven in the focus direction and the tracking direction. The PCB, serving as the supporting member 106, is connected to a control circuit (not shown) through a flexible printed circuit (FPC) 107 and a joining terminal 108.
A lens actuator L is constructed such that the lens holder 101 is provided with a focus driving coil 109 and a tracking driving coil 110, and the entire of the lens holder 101 is servo-controlled in the focus direction (the Y-axial direction indicated by an arrow) and the tracking direction (the X-axial direction indicated an arrow) by an electromagnetic driving manner using the interaction between the coils 109 and 110 and the magnetic field of permanent magnets 111a, 111b, 112a, and 112b fixed to the yoke base 103. In addition, the focus driving coil 109 is divided into two parts so as to additionally function as a driving coil for tilt servo control for adjusting the inclination of the lens holder 101 in the radial direction. In this case, the inclination of the lens holder 101 in the radial direction is adjusted by controlling the balance of a driving current to be supplied to the focus driving coils 109a and 109b. The technique of suppressing the inclination of the lens holder by adjusting the current passing through two focus driving coils is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 11-312327 (Patent Document 1).
The ends of the focus driving coil 109 and the tracking driving coil 110 are electrically connected to the six suspension members 105, respectively, and the other ends of the six suspension members 105 are held by a gel-type buffering material 113 filled in the suspension holder 104. In addition, the other ends thereof are soldered on a circuit board of the supporting member 106. Further, the six suspension members 105 are connected to both longitudinal end portions of the lens holder 101 at top, middle, and bottom positions in three pairs. For example, two top suspension members are connected to the focus driving coil 109a, two middle suspension members are connected to the focus driving coil 109b, and two bottom suspension members are connected to the tracking driving coil 110. In addition, a driving current is supplied through the suspension members 105 connected to the respective driving coils, based on the control information obtained from an optical disk.
As shown in FIG. 10, in the actuator assembly A having the above-mentioned cantilever supporting structure by the suspension members 105, the lens holder 101 is maintained in a horizontal state at normal temperature by the gel-type buffering material 113 filled in the suspension holder 104 and the supporting members 106. As a result, the beam spot of an optical beam concentrated on a recording surface 114a of an optical disk 114 is formed in an optimum circular shape.
In an optical disk device for recording information on an optical disk, the output level of an optical beam irradiated from the semiconductor laser hologram unit B or the semiconductor laser hologram unit C is generally composed of three kinds of levels, that is, a reproduction level, a removal level, and a recording level, and the respective output levels of the optical beam satisfy the following relationship: reproduction level<removal level<recording level.
When reproducing the information recorded on the optical disk 114, an optical beam of the reproduction level is irradiated from the semiconductor laser hologram unit B or the semiconductor laser hologram unit C and is then concentrated on the recording surface 114a of the optical disk. Since the optical beam of the reproduction level has the lowest output level, the optical beam does not much affect the ambient temperature of the actuator assembly A. Therefore, as shown in FIG. 10, the horizontal state of the lens holder 101 is maintained, and thus operating conditions thereof are stabilized.
However, when recording information on the optical disk 114, since an optical beam of the recording level having the highest output level is irradiated from the semiconductor laser hologram unit B or the semiconductor laser hologram unit C and is then concentrated on the recording surface 114a of the optical disk, the heat value of the semiconductor laser hologram unit B or the semiconductor laser hologram unit C increases, and the amount of heat generated from an LSI of an optical disk drive increases, which results in a burst increase in the ambient temperature of the actuator assembly A. The ambient temperature of the actuator assembly A when information is recorded on the optical disk 114 may rise up to ° Centigrade (140° Fahrenheit). When such a condition is maintained, the elasticity of the supporting member 106 having the floating structure and the holding force of the gel-type buffering material 113 are lowered by heat. Therefore, a floating portion of the supporting member 106 is bent by the weight of the lens holder 101 as shown in FIG. 9, which causes the lens actuator L to be inclined in the direction of gravitation (the jitter direction) as shown in FIG. 11. When the lens actuator L is inclined in the jitter direction, the beam spot of an optical beam concentrated on the recording surface 114a of the optical disk 114 has an elliptic shape, so that coma aberration occurs. As a result, the recording efficiency or reproducing efficiency of information deteriorates. Particularly, in an optical disk device for recording information DVD-type optical disks having high recording density, it is probable that the recording or reproduction of information will not be performed by the slight inclination of the lens actuator L caused by the variation of temperature.
Further, a method of controlling the inclination of the lens actuator in the jitter direction using the technique disclosed in Patent Document 1 can be considered. However, in this method, additional driving coils and magnets for controlling the inclination of the lens actuator in the jitter direction are needed, and these driving coils and magnets are incorporated into the optical disk device as shown in FIG. 7. That is, a separate control system for controlling the inclination in the jitter direction must be constructed, which results in an increase in the size of the optical pick-up device and a complexity of structure thereof.